Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 19-06-2023, 20:02   #1
Registered User
 
Renegde_Sailor's Avatar

Join Date: Dec 2018
Location: Washington
Boat: 1966 Spencer 42'
Posts: 341
Getting Screwed!

I have a propeller question...

Right now I am sailing my Spencer 42 to Alaska, she has a 12-8 pitch 19" 3 blade prop, I have noticed every time we wind up pushing through some waves running against us that the prop cavitates and the boat slows way down.

As well with my 40hp engine, it can easily spin the prop, I never have to run full throttle to get max speed because if I push it too far, it just cavitates.

I cannot go any bigger due to the aperture limiting the size, but I could go to a 4 bladed pitching prop like a MaxProp.

I am curious if anyone more knowledgeable than myself might have some insight on doing so, right now at 2200 rpm where the engine runs real nice, she will cruise at 6 knots, if I push her a bit harder she will clip along at 7.2 above that the prop just cavitates.

Or maybe it is not even worth messing with, but it would be nice if I could get a bit more speed under motor out of her without having to rev her so hard, it feels to me like she is under-propped, and I am wondering if going to a 4 blade would put her in better order when motoring against waves and current?
__________________
"I never saw a wild thing sorry for itself. A small bird will drop frozen dead from a bough without ever having felt sorry for itself." - D. H. Lawrence
Renegde_Sailor is offline   Reply With Quote
Old 19-06-2023, 20:50   #2
Registered User

Join Date: Jun 2011
Location: Caribbean
Boat: Hylas 46
Posts: 530
Re: Getting Screwed!

I have more questions first...

The size of your prop is not clear to me. It is 3 bladed. And the diameter is 19", right? So the pitch is what?

What is the condition of the prop? Is it clean, without growth on it? Any bent blades?

What is the maximum rated speed (rpm) of the engine? What the max eng speed you can reach, either limited by excessive cavitation or at WOT?

What type of prop is it: fixed, folding, feathering?
Lee Jerry is offline   Reply With Quote
Old 19-06-2023, 21:01   #3
Registered User
 
Renegde_Sailor's Avatar

Join Date: Dec 2018
Location: Washington
Boat: 1966 Spencer 42'
Posts: 341
Re: Getting Screwed!

Quote:
Originally Posted by Lee Jerry View Post
I have more questions first...

The size of your prop is not clear to me. It is 3 bladed. And the diameter is 19", right? So the pitch is what?

What is the condition of the prop? Is it clean, without growth on it? Any bent blades?

What is the maximum rated speed (rpm) of the engine? What the max eng speed you can reach, either limited by excessive cavitation or at WOT?

What type of prop is it: fixed, folding, feathering?

Fixed, I believe 19" and the number stamped on the side is 12-8 so I am assuming a 8" pitch? Prop is clean, was serviced and balanced last summer while the boat was out of the water.
__________________
"I never saw a wild thing sorry for itself. A small bird will drop frozen dead from a bough without ever having felt sorry for itself." - D. H. Lawrence
Renegde_Sailor is offline   Reply With Quote
Old 19-06-2023, 21:06   #4
Registered User
 
Renegde_Sailor's Avatar

Join Date: Dec 2018
Location: Washington
Boat: 1966 Spencer 42'
Posts: 341
Re: Getting Screwed!

I should add it might be a 18", I measured it when I pulled it, but that was about 50,000 projects ago!
__________________
"I never saw a wild thing sorry for itself. A small bird will drop frozen dead from a bough without ever having felt sorry for itself." - D. H. Lawrence
Renegde_Sailor is offline   Reply With Quote
Old 19-06-2023, 21:44   #5
Moderator
 
Pete7's Avatar

Cruisers Forum Supporter

Join Date: Aug 2009
Location: Solent, England
Boat: Moody 31
Posts: 18,595
Images: 22
Re: Getting Screwed!

Is this a new problem, or has it always been like this?

What is the clearance from the prop tip to the hull? should be at least 10% of the of the prop radius.

Problem with props is its a black art.

Pete
Pete7 is offline   Reply With Quote
Old 19-06-2023, 21:54   #6
Registered User

Join Date: Jul 2020
Location: SoCal
Posts: 694
Re: Getting Screwed!

you may still be able to get a larger prop by replacing your shaft for a longer one (IF you have space)
George_SD is offline   Reply With Quote
Old 19-06-2023, 21:59   #7
Registered User
 
Renegde_Sailor's Avatar

Join Date: Dec 2018
Location: Washington
Boat: 1966 Spencer 42'
Posts: 341
Re: Getting Screwed!

Quote:
Originally Posted by Pete7 View Post
Is this a new problem, or has it always been like this?

What is the clearance from the prop tip to the hull? should be at least 10% of the of the prop radius.

Problem with props is its a black art.

Pete

Well before this I had mostly sailed protected waters do I don't know as far as bashing through waves and having it cavitate.

The bottom job on my boat was hot trash and slowing it way down, she is much faster than what she used to be, I gained a knot and a half from when I pulled her out of the water to strip her.
__________________
"I never saw a wild thing sorry for itself. A small bird will drop frozen dead from a bough without ever having felt sorry for itself." - D. H. Lawrence
Renegde_Sailor is offline   Reply With Quote
Old 19-06-2023, 22:06   #8
Registered User
 
Renegde_Sailor's Avatar

Join Date: Dec 2018
Location: Washington
Boat: 1966 Spencer 42'
Posts: 341
Re: Getting Screwed!

I just pulled out my old survey, it says 16" 3 blade 12 pitch, but 12 seems pretty steep to me, the prop had numbers stamped on the side which I believe were 12-8
__________________
"I never saw a wild thing sorry for itself. A small bird will drop frozen dead from a bough without ever having felt sorry for itself." - D. H. Lawrence
Renegde_Sailor is offline   Reply With Quote
Old 19-06-2023, 22:07   #9
Registered User
 
Renegde_Sailor's Avatar

Join Date: Dec 2018
Location: Washington
Boat: 1966 Spencer 42'
Posts: 341
Re: Getting Screwed!

Quote:
Originally Posted by George_SD View Post
you may still be able to get a larger prop by replacing your shaft for a longer one (IF you have space)

Keel hung rudder with an aperture.
__________________
"I never saw a wild thing sorry for itself. A small bird will drop frozen dead from a bough without ever having felt sorry for itself." - D. H. Lawrence
Renegde_Sailor is offline   Reply With Quote
Old 19-06-2023, 22:10   #10
Registered User
 
Panope's Avatar

Join Date: Sep 2012
Location: Washington State
Boat: Colvin, Saugeen Witch (Aluminum), 34'
Posts: 2,284
Re: Getting Screwed!

What symptoms occur during the events you describe as "cavitation" ?

If the answer includes "a rise in engine rpm and loss of boat speed", then I would consider the possibility that the clutch in the gear box is slipping (assuming your gearbox has clutches), and that there is nothing wrong with the propeller.
Panope is online now   Reply With Quote
Old 19-06-2023, 22:24   #11
Moderator
 
Jim Cate's Avatar

Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 21,356
Re: Getting Screwed!

Another critical bit of info needed: what is the reduction ratio in the gear box?

Jim
__________________
Jim and Ann s/v Insatiable II, lying Port Cygnet Tasmania once again.
Jim Cate is offline   Reply With Quote
Old 19-06-2023, 22:30   #12
Registered User
 
Renegde_Sailor's Avatar

Join Date: Dec 2018
Location: Washington
Boat: 1966 Spencer 42'
Posts: 341
Re: Getting Screwed!

Quote:
Originally Posted by Jim Cate View Post
Another critical bit of info needed: what is the reduction ratio in the gear box?

Jim

Yanmar 4JH3E 36.8HP @ 3650 rpm (I run at 2200)

2.36 reduction
__________________
"I never saw a wild thing sorry for itself. A small bird will drop frozen dead from a bough without ever having felt sorry for itself." - D. H. Lawrence
Renegde_Sailor is offline   Reply With Quote
Old 19-06-2023, 22:32   #13
Registered User
 
Renegde_Sailor's Avatar

Join Date: Dec 2018
Location: Washington
Boat: 1966 Spencer 42'
Posts: 341
Re: Getting Screwed!

Quote:
Originally Posted by Panope View Post
What symptoms occur during the events you describe as "cavitation" ?

If the answer includes "a rise in engine rpm and loss of boat speed", then I would consider the possibility that the clutch in the gear box is slipping (assuming your gearbox has clutches), and that there is nothing wrong with the propeller.

Happens when I hit a wave, you can hear the bubbles on the prop under the boat.

Same as if you were starting from a standstill and gun it hard, you get the bubbles noise then as the boat comes up to speed it stops. Don't really see a rise in engine RPM.
__________________
"I never saw a wild thing sorry for itself. A small bird will drop frozen dead from a bough without ever having felt sorry for itself." - D. H. Lawrence
Renegde_Sailor is offline   Reply With Quote
Old 19-06-2023, 22:48   #14
Registered User
 
Panope's Avatar

Join Date: Sep 2012
Location: Washington State
Boat: Colvin, Saugeen Witch (Aluminum), 34'
Posts: 2,284
Re: Getting Screwed!

Quote:
Originally Posted by Renegde_Sailor View Post
Happens when I hit a wave, you can hear the bubbles on the prop under the boat.

Same as if you were starting from a standstill and gun it hard, you get the bubbles noise then as the boat comes up to speed it stops. Don't really see a rise in engine RPM.
Ok.

Rather than "cavitation" (the boiling of water due to extreme low pressure areas on the propeller face),

consider the possibility

that what you are experiencing is actually "ventilation" (air entering the propeller stream).

A friend of mine had an Islander 37 that had the propeller mounted very close to the surface. In waves the propeller would ventilate due to the boat pitching.
Panope is online now   Reply With Quote
Old 19-06-2023, 23:11   #15
Registered User
 
Renegde_Sailor's Avatar

Join Date: Dec 2018
Location: Washington
Boat: 1966 Spencer 42'
Posts: 341
Re: Getting Screwed!

Quote:
Originally Posted by Panope View Post
Ok.

Rather than "cavitation" (the boiling of water due to extreme low pressure areas on the propeller face),

consider the possibility

that what you are experiencing is actually "ventilation" (air entering the propeller stream).

A friend of mine had an Islander 37 that had the propeller mounted very close to the surface. In waves the propeller would ventilate due to the boat pitching.



I mean it is possible but I didn't think we were ramping that hard, these were 5-6' swells.

Here is a profile drawing of the boat.




Possible it could be venting as you said, I am going to have to pay more attention to it.
__________________
"I never saw a wild thing sorry for itself. A small bird will drop frozen dead from a bough without ever having felt sorry for itself." - D. H. Lawrence
Renegde_Sailor is offline   Reply With Quote
Reply

Tags
crew

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Am I getting screwed by yard? EmeraldCoastSailor Challenges 4 05-12-2018 13:47
Getting Screwed in NC CalChica Flotsam & Sailing Miscellany 22 22-06-2015 20:31
Non-Screwed Teak Decks FecklessDolphin Monohull Sailboats 21 16-10-2012 08:48
Fairleads Screwed or Thru-Bolted? rhr1956 Deck hardware: Rigging, Sails & Hoisting 11 24-02-2012 13:01
Last Change Has Screwed Up the Posting Boxes, Among Other Things DeepFrz Forum Tech Support & Site Help 10 29-12-2010 18:09

Advertise Here


All times are GMT -7. The time now is 11:06.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.